The invention relates to the measurement of adipose tissue using ultra-sonic methods, compositions and devices, particularly methods, compositions and devices that permit adjustment of parallax error associated with measuring layer thicknesses in a object, especially adipose tissue layers in a vertebrate.
Objects often include layers of different compositions that are difficult to measure directly and accurately. In many cases, the object""s interior can not be accessed to allow for direct measurement. It may be impractical to intrude the object""s interior or, if even using non-invasive techniques, it may be difficult to position the probe for accurate measurements.
For measurements of biological specimens, the thickness of underlying layers are particularly inconvenient to measure. Many such measurements are preferably taken in vivo, which makes invasive techniques impractical. If non-invasive techniques are used, they are often susceptible to operator errors and can be quite costly, as in the case of expensive medical diagnostic equipment.
In the case of body adipose tissue layers, measurements with skin calipers and water immersion tanks can be used to assess body adipose tissue. Such techniques, however, have a number of drawbacks.
Skinfold calipers use the principle that the amount of subcutaneous adipose tissue correlates to percent body adipose tissue (American College of Sports Medicine, ACSM""s guidelines for exercise testing and prescription, 53-63 (1995)). With a skinfold caliper measurement, after the skin is pinched by an operator without inducing pain to the subject, the thickness of the skinfold is measured with the caliper. Caliper measurements of skinfold thickness have been used with various equations developed to predict body density and percent body adipose tissue (American College of Sports Medicine, ACSM""s guidelines for exercise testing and prescription, 53-63 (1995)). Most of these equations, however, are sex-specific or only apply to certain populations. Other equations to estimate body density and percent body adipose tissue have been developed using regression models that can take into account data from larger population based studies (Jackson, A. S., Pollock, M. L., Br J Nutr, 1978: 497-504 (1978)).
Even with these improvements, however, skinfold calipers are subject to several serious sources of errors. First, skinfold caliper measurements are heavily operator dependent. The force used to pull back the skin by the operator and the location of the measurement site may vary significantly between different operators, or the same operator, resulting in poor reproducibility of measurements. Second, even though skinfold caliper measurements are based on the assumption that subcutaneous adipose tissue thickness correlates to percent body adipose tissue, skinfold calipers cannot measure the thickness of subcutaneous adipose tissue directly. Skinfold caliper measurements, instead, provide an estimate of subcutaneous adipose tissue thickness which, in turn, is then used to estimate percent body adipose tissue. Thus, two approximations are used to estimate percent body adipose tissue. Third, skinfold caliper measurements may overestimate subcutaneous adipose tissue thickness. When the skinfold is pulled back for the measurement, adipose tissue from adjacent sites can be pulled toward the measurement site causing an artificial increase in the amount of subcutaneous adipose tissue present in the selected body region. This problem is exaggerated in subjects with very elastic soft-tissue. Fourth, the inaccuracies associated with skinfold caliper measurements have lead to the use of equations requiring measurements of 3 body sites, 4 body sites, and even 7 body sites (American College of Sports Medicine, ACSM""s guidelines for exercise testing and prescription, 53-63 (1995)). However, even with these adjustments the inherent inaccuracies of skinfold caliper measurements, most importantly the inability to measure subcutaneous adipose tissue thickness directly, cannot be completely compensated.
Hydrostatic weighing is commonly considered the gold standard for determining body density and estimating percent body adipose tissue. Hydrostatic weighing relies on Archimedes"" principle. A body submerged in water is buoyed by a counterforce equal to the weight of the water that it displaced. Bone and muscle tissue are denser than water, while adipose tissue is less dense. Therefore, a person with low percent body adipose tissue will have higher body density and weighs more in water than a person with higher percent body adipose tissue and the same air weight. Conversely, a person with higher percent body adipose tissue for the same air weight will weigh less in water.
Although hydrostatic weighing is considered the gold standard for body adipose tissue determinations, it is subject to several sources of error. First, hydrostatic weighing requires estimation of pulmonary residual volume, which may vary significantly between individuals. Although pulmonary residual volume can be measured using pulmonary function tests, this adds extra time and expense to the procedure, which could decrease patient compliance. Second, hydrostatic weighing does not account for the variability in bone density known to exist between different individuals and races (American College of Sports Medicine, ACSM""s guidelines for exercise testing and prescription, 53-63 (1995)). In patients with high bone density, hydrostatic weighing will underestimate percent body adipose tissue. Conversely, in osteoporotic patients, hydrostatic weighing may seriously overestimate percent body adipose tissue. Third, hydrostatic weighing requires large and expensive displacement chambers, and complete patient immersion in water. The technical requirements and the expense of hydrostatic weighing limit its use in frequent longitudinal measurements of percent body adipose tissue that are desirable in ambulatory patients undergoing a nutritional regime or exercise induced adipose tissue reduction. Fourth, submersion of the head underwater may be difficult or anxiety provoking for some individuals.
Consequently, the present inventors have recognized the need to provide low cost and accurate ultra-sonic devices and methods for such applications, particularly hand held devices capable of being operated by untrained operators. Methods and devices are provided herein to provide for cost effective measurements and accurate of layer thickness, such as adipose tissue layer thickness.
The present invention provides for the convenient and cost effective measurement of layer thickness in an object, such as adipose tissue thickness in a human, using the appropriate ultra-sonic wave production and signal processing described herein. Previously, it was not recognized that ultra-sonic measurements of layer thickness of an object were subject to inaccurate measurements due to parallax error. Nor was it previously recognized that ultra-sonic devices dedicated to measurement of layer thickness at short interrogation depths, particularly hand-held devices for self-measurement of body adipose tissue, could accurately determine layer thickness.
Non-orthogonal ultra-sonic probe alignment with respect to the plane of the interrogated object can produce an error in the measurement of layer thickness, particularly layer thickness measurements at short interrogation depths. Non-orthogonal probe alignment typically occurs when the probe transmission axis is less than 90 degrees with respect to the object plane, which has a reference angle xcex2 of 0 degrees as shown in FIG. 1. When the transmission angle is less than 90 degrees, the probe transmits and receives ultra-sonic waves over a longer than intended path that can traverse an underlying layer (or layers) of an object, which can lead to a transmission parallax error in estimating layer thickness.
The present invention provides for a method of measuring layer thickness in an object comprising: 1) transmitting at least a first and a second ultra-sonic pulse from at least a first position and a second position, 2) measuring at least one reflective distance from the first pulse and at least one reflective distance from the second pulse, wherein the reflective distance is from the object""s external surface (or probe) to a reflective interface of at least one layer, 3) selecting the reflective distance having the shortest reflective distance to indicate the distance between the external surface (or probe surface) and the reflective interface of at least one layer, wherein the selecting of the shortest reflective distance reduces ultra-sonic transmission parallax of the first and second pulses relative to a plane in the object.
In another embodiment, the invention provides for a method of measuring body adipose tissue, comprising 1) transmitting at least a first and a second ultra-sonic pulse from at least a first and second position, 2) measuring at least one reflective distance from the first pulse and at least one reflective distance from the second pulse, wherein the reflective distance is from the skin to 1) an adipose tissue/muscle or 2) an adipose tissue/fascia interface, and 3) selecting the reflective distance having the shortest distance to calculate the distance between the inner or outer border of subcutaneous adipose tissue, wherein the selecting of the reflective distance helps correct for an ultra-sonic transmission parallax of the first and second pulses relative to a plane in the subcutaneous adipose tissue.
The invention can include three different methods (with the corresponding devices) for varying the transmission angle: 1) mechanically changing position of the transducer(s), 2) providing multiple transducers with predetermined positions that correspond to predetermined transmission angles and 3) steering ultra-sonic beams from multiple ultra-sonic sources (typically arrays) with predetermined firing sequences.
In one embodiment, the invention provides for a compact, cordless hand held device comprising a first ultra-sonic source with a first detector that receives an alpha ultra-sonic signal and the second ultra-sonic source with a second detector that receives a beta ultra-sonic signal. The first and second ultra-sonic detectors may be configured to detect the alpha or the beta ultra-sonic signals either individually or collectively. The first ultra-sonic source provides for a pulse with a first transmission angle and the second ultra-sonic source provides for a pulse with a second transmission angle, wherein the second transmission angle improves the measurement of a shortest reflective distance compared to the measurement of a shortest reflective distance in the absence of the second transmission angle. Alternatively, the first and second ultra-sonic sources are at least one linear array of ultra-sonic crystals that can be sequentially timed to improve measurement of the shortest reflective distance compared to the measurement of the shortest reflective in the absence of the sequential timing. Preferably, the ultra-sonic system is contained within a autonomous, hand-held housing that does not require an external connection to another device. Such devices are particularly useful for self-examination by individuals.
The ultra-sonic system may optionally comprise a computational unit that corrects for nonorthogonal probe alignment, wherein the computational unit permits computational determination of a shortest reflective distance. Typically, the computational unit will be a chip programmed to calculate reflective distance and the shortest reflective distance. For example, the computational unit can be programmed to calculate the shortest reflective distance in a human based on reflective distances from the 1) a skin/adipose tissue interface and 2) an adipose tissue/muscle or adipose tissue/fascia interface.